Primed substrates are used in many industries in order to better adhere overlying layers, patterns, or text. The term “primed” generally refers to the use of a coating, usually a dried polymeric coating, which has good adhesion both to the underlying substrate of a desired smoothness and composition and to overlying materials.
For example, patternable materials can be used in various industries to provide patterns of conductive or non-conductive lines, solid areas, text, grids, electrical circuits, or other shapes. Relief printing members can be used to apply these patterns to various substrates, and the resulting patterns can be further treated to provide electrical conductivity or other properties for use in the electronics, display, or energy industries. For example, electrically-conductive patterns can be designed and prepared on transparent substrates for use in various display devices for example as touch screens.
Polyester and other polymeric films have been well known for decades as useful substrates on which coatings or patterns have been applied. Polymeric films (or articles) of this type are often more suitable for various purposes including printing members, imaging elements, and display devices because of their strength, flexibility, and potential transparency. However, a practical difficulty often arises, depending upon the materials to be applied, in the course of attempting to produce and maintain strong adhesive forces between the polymeric substrates and overlying coatings or patterns because the polymeric substrates are generally highly hydrophobic and overlying coatings or patterns may be less hydrophobic in nature. Alternatively, the polymeric substrates can less hydrophobic than the overlying coatings or patterns.
Many problems arise from poor adhesion in various industries. Touch sensitive panels or displays require very fine lines (on the order of less than 20 μm in width) in predetermined patterns to achieve desired electrical conductivity simultaneously with high visual transparency (or high integrated transmittance).
When adequate adhesion is not achieved or maintained during manufacture and use of fine lines of electrically-conductive materials including electrically-conductive metals or metal precursors, desired electrical-conductivity or capacitance is not achieved. U.S. Patent Application Publication 2007/0170403 (Conaghan et al.) describes these adhesion problems and some proposed solutions by using various adhesive or primer layers on substrates or the incorporation of adhesion promoting compounds into applied conductive “inks” (compositions).
For example, adhesion and various surface properties of flexible and transparent substrates can be improved using polymeric primer layers applied to supporting surfaces of polymeric films. The desire is to better adhere later applied materials especially when those materials are applied in a uniform fashion. Examples of primer layer compositions used for this purpose are described for example in U.S. Pat. No. 6,162,597 (Bauer et al.) and U.S. Pat. No. 6,165,699 (Bauer et al.).
Moreover, U.S. Patent Application Publication 2013/0319275 (Fohrenkamm et al.) describes a means for improving flexographic printed conductive lines by designing the substrate and printed ink to have a unique polarity relationship.
The production of touch screen sensors and other transparent conductive articles in roll-to-roll production methods on flexible and transparent substrates using “additive processes” for deposition of electrically-conductive patterns that provide the functionality of the sensor has been the subject of recent development in the industry. Of particular importance is the ability to produce a touch screen sensor that has both the desired electrical performance as well as appropriate optical properties (transmittance) in the visible portion (touch region) of the touch screen sensor. To achieve the necessary conductive and optical properties, average line widths of electrically-conductive lines in the electrically-conductive grid of less than 10 μm are greatly desired.
The flexible and transparent substrates used in such processes should be optically clear (high integrated transmittance) and colorless and exhibit low haze. The application of electrically-conductive patterns using additive processes such as flexographic printing of electrically-conductive materials or seed metal compositions requires the flexible and transparent substrate to have appropriate surface energy and roughness consistent with the scale of the fine features (for example, fine lines) to be applied. Considerable effort is being exerted in the electronics industry to achieve these necessary features.
WO 2013063188 (Petcavich et al.) describes a method for producing a mutual capacitance touch sensor comprising a dielectric substrate by printing, using a flexographic printing process with at least a first master plate and a first ink, a first pattern on a first side of a dielectric substrate; and curing the printed dielectric article. A second ink can be similarly applied and cured to form a second pattern on a second surface of the substrate. Both patterns can then be electrolessly plated with a conductive material. The resulting dielectric article is described to have a thickness of 1 μm to 1 mm and a preferred surface energy of from 20 Dynes/cm to 90 Dynes/cm.
Continued efforts are being directed to finding a cost effective way to provide flexible and transparent substrates having the desired surface and optical properties for various electronic devices such as touch screen sensors and other optical displays. These efforts are particularly directed at making and using such substrates in high efficiency roll-to-roll manufacturing operations in which the substrates are subjected to various chemical and mechanical operations.
In particular, there is a need in the art for flexible and transparent substrates that exhibit low haze, low color, and surface uniformity and are thus more suitable for adhering fine features such as thin lines, text, or small shapes, and are particularly suitable for fine lines that are electrically-conductive. Flexible and transparent substrates are also desirable that exhibit strong adhesion to “printed” patterns such as those applied by flexographic printing of metal-containing compositions that are inherently or can be further treated to become electrically-conductive.